1. Field of the Invention
The present invention relates to a solid-state imaging device capable of focus adjustment of a phase detection method.
2. Description Related to the Prior Art
An autofocusing function has become a standard feature of camera modules of mobile electronic devices such as digital cameras, mobile phones, and smartphones. Types of autofocusing functions include a contrast detection type (the so-called contrast AF) that performs focus adjustment to make the contrast of the image maximum and a phase detection type (hereinafter referred to as the phase detection AF) that performs the focus adjustment based on a phase difference caused by parallax. Although the contrast AF requires finding an inflection point while a taking lens is moved, the phase detection AF enables fast autofocusing because it detects the focus state at each lens position.
For example, as described in Japanese Patent Laid-Open Publication No. 2012-003009, in the solid-state imaging device which performs the phase detection AF, two types of phase detection pixels (right phase detection pixels and left phase detection pixels) are disposed in a predetermined pattern. Each of the two types of the phase detection pixels selectively receives the light incident from right or left direction. The focus adjustment is performed by calculating information related to the phase difference based on pixel signals (pixel values) obtained from the two types of phase detection pixels and driving the taking lens so as to reduce the phase difference. In the Japanese Patent Laid-Open Publication No. 2012-003009, the phase detection pixel is formed by making the color filter asymmetrical in a left-right (side-to-side) direction. A phase detection pixel with an opening off-centered relative to the center of a corresponding photodiode and a phase detection pixel formed by making an inner-layer lens asymmetrical have also been known.
A monocular 3D imaging device that takes two perspective images for stereoscopy at a time with one solid-state imaging device has been known. All of the pixels disposed in the light receiving area of this solid-state imaging device are perspective pixels each with two photodiodes placed side by side behind one on-chip microlens. Each of the two photodiodes has approximately half the size of that of a normal pixel. The two photodiodes constitute a right perspective pixel portion for imaging a right perspective image and a left perspective pixel portion for imaging a left perspective image (see U.S. Pat. No. 8,772,892 corresponding to WO 2012/026292).
A solid-state imaging device in which phase detection pixels (hereinafter may referred to as the measurement pixels) are arranged at predetermined positions in the light receiving area has been known. Each measurement pixel is provided with two or more transparent electrodes for control so as to virtually divide one measurement pixel into two or more regions (see Japanese Patent Laid-Open Publication No. 1-215063). In the measurement pixel, each transparent electrode is controlled independently, so that a signal is read out independently from each region, to be used for metering and color temperature detection.
Each phase detection pixel has a shape asymmetrical in, for example, the left-right direction, so that a pixel signal obtained from the phase detection pixel differs from that obtained from a symmetrically-shaped normal pixel. For this reason, the pixel signal of the phase detection pixel cannot be used for producing a normal image in a case where an image of a subject is taken after the phase detection AF. It is necessary to generate the pixel signal, for the normal image, corresponding to the position of the phase detection pixel through gain correction of the pixel signal of the phase detection pixel or interpolation using the pixel signals of the adjacent normal pixels. In the case where the pixel signal for the normal image is generated by the gain correction or the interpolation, sensitivity or resolution of the pixel corresponding to the position of the phase detection pixel may be substantially reduced depending on the specific properties of the subject and accuracy of the gain correction, the interpolation, or the like.
Some of the current camera modules, digital cameras, and the like are provided with a mode for taking a movie and a mode for performing pixel addition. However, the solid-state imaging device having the phase detection pixels may not be allowed to adopt such modes because the phase detection pixels may degrade the image quality of normal images. The accurate focus adjustment by the phase detection AF may sacrifice some of other convenient features of the solid-state imaging device.
In a 3D imaging device with the phase detection pixels disposed all over the light receiving area, the phase detection AF is performed by using signals from right pixel portions and signals from left pixel portions. In order to produce a normal image (2D image), it is necessary to use one of right perspective image and left perspective image or average or add the pixel signals of the right and left pixel portions. In this case, however, the number of pixels for producing the normal image is half the total number of the left and right pixel portions arranged in the light receiving area, so that the resolution of the normal image becomes low. Each of the right and left perspective images is produced using pixel signals all obtained from the asymmetrically-shaped pixels. As a result, the sensitivity is inferior to that of the case where imaging is performed with the normal pixels, which receive light evenly from every direction.
With regard to the measurement pixel described in Japanese Patent Laid-Open Publication No. 1-215063, one pixel is virtually divided into two or more regions. For example, a signal is taken out separately from each of a right half region and a left half region of a pixel to perform the phase detection AF. However, color filters of different colors are disposed to the respective regions, so that the signal the same as that of the normal pixel cannot be obtained even if the signals are read out from each region of the measurement pixel at the time of producing a normal image. Even in the Japanese Patent Laid-Open Publication No. 1-215063, the correction of the pixel signal from the measurement pixel is necessary to obtain the pixel signal for producing a normal image, resulting in partial reduction in resolution and sensitivity.